Stabilized soap



Patented Feb. 18, 1947 STAPILIZED SOAP Myers F. Gribbins, Wilmington, Dcl., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 19, 1945, Serial No. 583,637

14 Claims.

The present invention relates to stabilized soaps, to the manufacture of stabilized soap and soap products and especially stabilized soap and soap products made from ingredients, one or more of which ordinarily deteriorate or develop rancidity in a relatively short time and particularly to soap stabilization by substituted beta mercaptopropionic acid or its derivatives.

It is well known that soaps tend to become rancid and discolor after storage. It is not definitely known just what causes the deterioration but it has been suggested that it may be due to oxidation or chemical decomposition. Such deterioration is highly objectionable as it renders the soaps unattractive by blanketing in many instances the perfumes of the soap discoloring it and/or leaving an objectionable rancid odor on the skin or the article being cleaned. Many attempts have been made to overcome this deterioration, the addition of various substances having been proposed to inhibit or retard it.

An object of the present invention is to provide stabilized soaps. Another object is to provide compounds to be incorporated in the salts of fatty acids Which will retard or inhibit their deterioration or prolong the period during which the salts are not rancid, which period is commonly referred to as the induction period, the salts so treated being free from the disadvantageous properties of compounds heretofore employed for this purpose. Still another object is to provide substituted beta mercaptopropionic acids and their esters as soap rancidity inhibitors. Other objects and advantages of the invention will appear hereinafter.

These objects may be accomplished in accordance with the invention by stabilizing liquid, jell-like and cake soap against rancidity by the incorporation therein of substituted beta mercaptopropionic acids or esters, by which is meant compounds containing the group ikyl groups: methyl, ethyl, propyl, butyl, lauryl,

and the aryl groups: phenyl, naphthyl, benzyl; and such groups as p methoxy phenyl, p hydroxy phenyl and cyclohexyl, which gives respectively:

a. B-methyl mercaptopropionic acid b. 3-ethyl mereaptopropionic acid c. 3-propy1mercaptopropionic acid 3-butyl mercaptopropionic acid 3-laury1 mercaptopropionic acid B-phenyl mercaptopropionic acid 3-benzyl mercaptopropionic acid 3-naphthyl mercaptopropionic acid B-(p methoxy) phenyl mercaptopropionic acid 3-(p hydroxy) phenyl mercaptopropionic acid 3-cyclohexyl mercaptopropionic acid Compounds of this type may'be prepared by the addition of mercaptans to acrylonitrile followed by acid or alkaline hydrolysis of the nitrile group to produce the desired product.

6. f. h. i. 7'. k.

Example.-3-ethylmercaptopropionic acid preparation 3-ethyl mercaptopropionic acid properties: Formula: CHsCHz-S-CHzCHzCOOH. Molecular Weight: 134. Boiling point: 93 C./2 mm. Neutral equivalent: 134. Solubility in water 20 C.: slightly soluble. Solubility in fats 20 C.: fairly soluble. Appearance: water white liquid.

HOOCCHzCHzSCHzCHaCHzOH :1. 3-methoxymethyl mercaptopropionic acid HOOCCHzCHzSCHzOCHs e. 3-methoxy'ethyl mercaptopropionic acid HOOCCHzCHzSCI-IzCI-IzOCI-Is f. 3-ethoxyethyl mercaptopropionic acid HOOCCHzCHzSCI-IzCHzOCzHs g. 3-carboxymethyl mercaptopropionic acid HOOCCHzCHzSCI-IzCOOH ht B-carboxyethyl mercaptopropionic acid (betabeta thio-dipropionic acid) HOOCCHzCHzSCHzCHzCOOH i. 3-carboxypropyl mercaptopropionic acid HOOCCHzCHzSCHzCHzCHzCOOH a. B-carboxybutyl mercaptopropionic acid HOOCCH2CH2SCH2CH2CH2COOH k. 3-aldehydoethyl mercaptopropionic acid HOOCCHzCHzSCHzCHzCHO The type reaction is identical to that indicated in section 1. Specifically, oxygenated mercaptans are added to acrylonitrile and the nitrile group hydrolyzed by acid or alkaline treatment.

Example-3 hydrozcyethyl mercaptopropionic acid preparation 2'7 parts (0.35M) mercapto glycol (HSCHzCHzOI-I) is added to 19 parts (0.35M) of acrylonitrile in the presence of 0.5 part piperidine. The reaction mixture is topped to remove unreacted mat-erials and then heated in an excess of concentrated HCl ('75 parts) for 1 hour. The by-product NH4C1 precipitates out and is removed by filtration. Excess HCl and H20 are removed by vacuum treatment. The product,

HOCI-IzCI-IzSCHzCHzCOOI-I is a water white, thick liquid which decomposes on distillation. Neutral equivalent=l50.

3. A sulfur-hydrocarbon group such, e. g., as: mercaptoethyl, mercaptopropyl, mercaptobutyl, mercaptoisobutyl, mercaptohexyl and ethiaethyl, which gives respectively:

a. 3-mercaptoethyl mercaptopropionic acid HOOCCH2CH2SCH2CH2SH b. 3-mercaptopropyl mercaptopropionic acid HOOCCH2CH2SCH2CH2CH2SH c. 3-mercaptobutyl mercaptopropionic acid HOOCCH2CH2SCH2CH2CH2CH2SH d. 3-mercaptoisobutyl mercaptopropionic acid nooccnzcmscmomcnsn e. 3-mercaptohexyl mercaptopropionic acid HOOCCHzCHzSCeHmSH ,f. Ethiaethyl mercaptopropionic acid HOOCCH2CH2SCH2CH2SC2H5 The type reaction is identical to that indicated in Section 1. Specifically, it involves the addition of molar amounts of dimercaptans to acrylonitrile,'followed by acid or alkaline hydrolysis of the nitrile group.

Ezample.6-mercapto 4 thiaheamnoic acid preparation To a solution of 329 parts (3.5M) ethanedithiol and 2 parts piperidine in 450 parts ethyl alcohol, 185.5 parts (3.5M) acrylonitrile is added dropwise over a period of 1 hour. Reaction tempera ture is maintained between 40-50 C. A precipitate of the di-addition product forms and is removed by filtration. Distillation of the filtrate gives the desired product HSCH2CH2SCH2CH2CN boiling point 139-141 C./6 mm. in about 26% yield. Heating 20 parts of this nitrile in parts concentrated HCl for 2 hours (in steam bath) produces the final product, a light yellow liquid, boiling point 142-1 13 C./2 mm. Neutral equivalent=166.

4. A sulfurand oxygenated-hydrocarbon group such, e. g., as: Carboxyethiaethyl,

-CH: .CH2SCH2CH2COOH Carboxyethiaethdithiaethyl,

I -CH2CH2SSCH2CH2SCH2CHzCOOH Carboxyethiaisobutyl, V

-CH2CH2CH (CH3) SCHzCHzCOOI-I and Carboxyethiapropyl,

which gives respectively:

a. 4,7-dithiasebacic acid HOOCCH2CH2S-CH2CH2SCH2CH2COOH b. 4,7,8,l1-tetrathiatetradecandioic acid c. 5 methyl-4,8-dithiaundecandioic acid HOOCCHzCHzSCHzCI-IzCH CH3) SCHzCI-IzCOOH d. 4,1l-dithiatetradecanedioic acid HOOCCH2CH2S(CH2) eSCHzCHzCOOH Type reaction is identical to that indicated in. Section 1. Specifically, it involves the addition of 2 moles acrylonitrile and 1 mole of a dimercaptan to give a sulfur containing dinitrile which can be hydrolyzed by acid or alkaline treatments.

Example.-4,7-dithiasebacic acid preparation Formula: I

HOOCCH2CH2SCH2CH2--SCH2CH2COOH Molecular weight: 236.

M. P.: 151 C.

Neutral equivalent: 118.

Solubility in water 20 0.: very slightly soluble. Solubility in fat 20 0.: slightly soluble. Appearance: odorless white crystals.

5. Or a sulfur-,

nitrogen-hydrocarbon group. such, e. g., as: 3-benzothiazyl mercaptopropionic acid CS-GHaCHsCOOH Emample.-3-benzothiazyl mercaptopropionic acid preparation To a solution of 167 parts (1M) mercaptobenzoties:

Formula Molecular weight: 239.

M. P.: 149-l50 C.

Neutral equivalent: 239.

Solubility in water 20 C.: slightly soluble. Solubility in fat 20 0.: slightly soluble. Appearance: white crystals.

'I'hesestabilizers may be incorporated in the soap in any suitable manner such, for example, as by simple mixing in proper proportions into the liquid or gel-like soap, by grinding, malaxing, or thoroughly and uniformly distributing it into the more or less solid soaps, the latter being subsequently formed'intc solid cakes or other shapes. Alternatively the stabilizers may be added at any convenient stage in the process of soap manufacture, care being exercised not to add it at a stage which will result in decomposition, leaching, or deterioration of the stabilizing agent. If desired, for example, these agents may be added during the well known crutching operation.

The stabilizers may be present in the soap to the extent of as little a 0.005%. The inhibiting powers of the particular agent used, or if a mixture is used, then the power of the mixture of agents will determine the exact amount that should be used for any desired duration of stabilization. The optimum amount to be used may be determined for any agent or mixture by preparing a series of compositions containing selected amounts for example from 0.005% to say 5% of the agent or mixture such as 0.001, 0.01, 0.1, 1.0, 2.5, and 5% or a more comprehensive serie with smaller diiferentials if desired, placing these compositions under controlled storage conditions for the number of days the composition is to be maintained in the stabilized state. The composition that contains the minimum amount of stabilizing agent is the amount that should be used to stabilize the soap for the selected period. Amounts ranging from .01 to about 2% give excellent stability to the soap.

The stabilizers may be used in soaps generally for there are few if any that do not require some stabilization. The strong laundry soaps rancidify leaving undesirable odors. The delicate, more highly purified facial soaps likewise rancidify to destroy the perfume used. As example of the soaps that can be stabilized by these agents are included the alkali metal and alkaline earth metal as well as the heavy metal salts of the higher fatty acids and mixtures of salts of such acid and complex alcohols obtained by the saponiflcation of the marine, vegetable, and animal oils and fats. The stabilizers are effective in watersoluble, water-insoluble and metallic soaps; the so-called mineral oil soaps, i. e., the water-soluble mineral oils and the like which are generally mixture of mineral oils and oil soluble. soaps which are used without water as a coolant in the machine tool industries and with water in the form of an emulsion as a coolant for cutting tools and as an insecticide spray; and in cosmetics compositions generally containing soaps which are used in tooth pastes, faceand body creams, e c.

The surprising and unexpected stabilizing effect of the substituted beta mercaptopropionic acids and their derivatives is clearly demonstrated by the following tests. The test involves the examination of soap with and without the stabilizer for color, peroxide value and odor. The color is determined by visual examination; the peroxide value as included in the Swift test (Oil and Soap 10, -109, 1933), and the odor by placing aliquot portions of the soap with and without stabilizer in stoppered flasks of equal size, storing them under a constant temperature of about 50 C. At the end of each day, the stopper was remove and any odor indicating rancidity noted. The soap was combined with the stabilizer by malaxing the soap at about room temperature with the stabilizer. Table I tabulates the result of observations.

Table I Peroxide Treatment Days Color value Odor 1 White... 1.8 None. 1 .do 2. 4 Do. 4 Brown 9. 2 Rancid. 4 White.. 2. 8 None. 10 Brown 21. 0 Rancid. 10 mi. 2. 8 Slightly rancid.

A. Soap with no stabilizer. B. Soap with 1% thiodipropionic acid.

The stabilizers described under the 5 groups and their equivalents may be used as the acid, ester or salt. Generally as specific examples of the esters may be included the methyl, ethyl N- and iso-propyl, N- and iso-butyl and the higher straight and branched chain alkyl esters as well as the alicyclic ester cyclohexyl. As specific examples of the salts are included the alkali metal and alkaline earth metal salts and particularly the sodium, potassium, calcium and magnesium salts.

I claim:

1. A process which comprises protecting soap against rancidity by incorporating therein a compound selected from the group consisting of 3-hydrocarbon substituted mercaptopropionie acids, their esters and salts.

2. A process which comprises protecting soap against rancidity by incorporating therein a compound selected from the group consisting of 3-oxygenatecrhydrocarbon substituted mercaptopropionic acids. their esters and salts.

3. A process whicicomprises protecting soap 7 against rancidity by incorporating therein a com pound selected from. the group consisting 01 v 3-sulfur hydrocarbon substituted mercapto-propionic acids, their esters and salts.

4. A process which comprises protecting soap against rancidity by incorporating therein a compound selected from the group consisting of 3-sulfurand oxygenated-hydrocarbon substituted mercaptopropionic acids, their esters and salts.

5. Soap stabilized against rancidity b a compound selected from the group consisting of 3-hydrocarbon substituted mercaptopropionic acids, their esters and salts.

6. Soap stabilized against rancidity by a compound selected from the group consisting of 3-oxygenated hydrocarbon substituted mercaptopropionic acids, their esters and salts.

7. Soap stabilized against rancidity by a compound selected from the group consisting of 3- sulfur-hydrocarbon substituted mercaptopropicnic acids, their esters and salts.

8. Soap stabilized against rancidity by a compound selected from the group consisting of 3-su1furand oxygenated-hydrocarbon substituted mercaptopropionic acids, their esters, and salts.

9. A soap comprising a water soluble salt of a higher fatty acid stabilized against deterioration and development of rancidity by having incor- 8 porated therein more than 0.005% of a compound selected from the group consisting of S-hydrocarbon substituted mercaptopropionic acids, their esters and salts.

10. A soap comprising MYERS F. G'RI'BBINS.

REFERENCES crrEn The following references are of record in the file of this patent: w

UNITED STATES PATENTS Name Date Gribbin et a1. Apr. 9, 1946 Number v a water soluble salt 01 of a higher fatty acid stabilized against deterioraand r 

